Predicting long-term creep failure of bimodal polyethylene pipe from short-term fatigue tests

Short-term fatigue testing was used to predict long-term creep failure of a bimodal polyethylene (BMPE) pipe with superior creep resistance. The stepwise crack propagation was studied by increasing the R-ratio (defined as the ratio of the minimum to the maximum stress intensity factor in the fatigue loading cycle) at 50 °C from 0.1 approaching creep (R = 1). Crack growth rate (da/dt) was related to the maximum stress intensity factor KI,max and R-ratio by a power law relationship \( {\frac{{{\text{d}}a}}{{{\text{d}}t}}} = B^\prime K_{{{\text{I}},\max }}⁴ (1 + R) ^{- 8.5} \). The correlation in crack growth kinetics allowed for extrapolation to creep fracture from short-term fatigue testing. The temperature dependence of crack growth rate was contained in the prefactor B′. A change in slope of the Arrhenius plot of B′ at 67 °C indicated that at least two mechanisms contributed to crack propagation, each dominating in a different temperature region. This implied that a simple extrapolation to ambient temperature creep fracture from elevated temperature tests might not be reliable.